1. Field
The present invention relates to wireless communication, and more particularly, to an apparatus and method for performing handover in a multiple component carrier system.
2. Discussion of the Background
Cellular is a concept proposed to overcome limits to a service area and limits to capacities to accommodate the frequency and subscribers. That is, a mobile communication service area is classified into several small cells, different frequencies are allocated to neighbor cells, and the same frequency band is used in two cells without interference sufficiently spaced apart from each other so that the frequency can be spatially reused.
The term ‘handover’ or ‘handoff’ refers to a function of, when a User Equipment (UE) goes out of a current communication service area (hereinafter referred to as a ‘serving cell’) and moves to a neighbor communication service area (hereinafter referred to as a ‘neighbor cell’), the UE is automatically tuned to a new traffic channel of the neighbor communication service area so that the traffic state remains intact. When handover is performed, a call disconnection problem occurring when a UE moves to a neighbor cell can be solved.
In general, a wireless communication system uses one bandwidth for data transmission. In order to increase a transmission capacity, to increase the bandwidth may be said to be indispensable, but to support a great bandwidth even when a required service level is low may result in great power consumption.
In order to solve the problem, a multiple component carrier system for defining a carrier having one bandwidth and the center frequency and sending or receiving or both data through a plurality of carriers in a broadband way is emerging. When one or more carriers are used, a narrowband and a broadband can be supported at the same time.
In the prior art, however, a BS has only to perform handover by taking a single cell, measured and reported by a UE, into account because only handover in a BS using a single component carrier is taken into consideration.
If handover is performed in a multiple component carrier system, multiple component carriers have to be taken into consideration. A target BS needs to perform a handover procedure such that a UE can use component carriers necessary to maintain Quality of Service (QoS) of a level provided by a source BS. However, there is a problem in that it is difficult for the target BS to configure adequate component carriers or component carriers of an adequate level because the target BS is unable to accurately know a service providing situation for the UE prior to the handover procedure. In order to solve the problem, there is provided a handover scheme in which multiple component carriers are taken into consideration.